A great many different operating strategies and component designs are known from the field of internal combustion engines. Research and development has progressed for decades in relation to the manner in which factors such as fueling, exhaust gas recirculation, turbocharging, and variable valve actuation can be varied to produce different results. In addition to variation in these and other operating parameters, a great deal of research and testing effort has gone into the different ways that engine components, such as pistons, can be shaped and proportioned, and formed from various materials. One motivation driving advancements in combustion science and related research has been the desire to reduce relative amounts of certain emissions in engine exhaust, such as particulate matter and oxides of nitrogen or NOx. Other motivations relate to improving or optimizing performance, reducing fuel consumption, or still other ends.
It has long been known that engine duty cycle, generally understood as the patterns of use of an engine under field service conditions, can affect the way in which engine components perform and tolerate real world operation. Duty cycle also affects the extent and manner in which exhaust emissions, fuel consumption, and other performance variables respond to adjustments in the various controllable operating parameters. Some engines are operated at so-called low idle or medium idle conditions with only relatively minor variations in engine speed or engine load in the standard or expected engine duty cycle. As such, engineers may design engine components and establish operating parameters and expectations that are based upon the relatively stable operating points that are expected.
Other engine duty cycles are more dynamic, where the engine speed or engine load, or both, are routinely varied, sometimes to a significant degree. A diesel internal combustion engine in a transit locomotive, for example, could be increased in engine speed or engine load up to or close to a rated engine speed or engine load between stops or stations, but dropped to low idle conditions while the locomotive is stopped for passenger loading and unloading. One can imagine the transit locomotive engine experiencing relatively rapid and wide swings in such factors as temperature and in-cylinder pressure. Still other engine duty cycles may be much less predictable, and the engine can operate for long periods of time at high idle, relatively long periods of time at low idle, and then be rapidly ramped up and ramped down between higher speeds and loads and lower speeds and loads for a period of time.
Efforts to accommodate the various different patterns of engine operation and duty cycle have resulted at least in part in the great many engine operating strategies and component designs that can be seen in the art. For certain engines that are subjected to relatively harsh operating conditions, and notably frequent temperature swings, one area of research and development interest has included refinements in piston geometry and materials that can tolerate high temperatures and/or otherwise intense thermal fatigue-inducing conditions. Other research efforts have contemplated pistons that are well suited to conditions of relatively extreme mechanical duress. Commonly owned U.S. Pat. No. 6,155,157 to Jarrett is directed to a piston formed of two pieces structured to increase piston longevity where increased forces of combustion are experienced. Jarrett proposes a piston with a head member and a separate skirt member, joined together by inertia welding. The force of combustion acting on a crown portion of the head member is resisted by a support surface of a ring band. The skirt member is stated to resist the bending moment of the combustion forces on the head member.